This invention relates generally to medical imaging systems and methods and more particularly to system and methods for adjusting noise in the medical imaging systems.
Typically, in computed tomography (CT) imaging systems, a gantry includes an X-ray source that emits a fan-shaped beam toward an object, such as a patient. The beam, after being attenuated by the patient, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the X-ray beam by the patient. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing unit for analysis which ultimately results in a formation of an image.
Generally, the X-ray source and the detector array are rotated with a gantry within an imaging plane and around the patient. X-ray sources typically include X-ray tubes, which conduct a tube current and emit the X-ray beam at a focal point. X-ray detectors typically include a collimator for collimating X-ray beams received at the detector, a scintillator for converting X-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator.
The CT imaging systems use a projection area or projection data from a scan acquisition, such as a scout scan, to determine a tube current per rotation of the gantry that maintains a constant noise independent of patient sizes of a first, second, and a third patient. For example, a CT scanner manufactured by a manufacturer A provides a first constant noise and a first tube current independent of the patient sizes scanned by the scanner. Another CT scanner manufactured by a manufacturer B provides a second constant noise and a second tube current independent of the patient sizes scanned by the scanner. However, if the CT imaging systems scan the second patient that may be larger than the first patient by applying the same amount of tube current as that applied to the first patient, quality of images of the second patient is degraded by image noise. On the other hand, if the CT imaging systems scan the third patient that may be smaller than the first patient by applying the same amount of tube current as that applied to the first patient, quality of images of the third patient may not be degraded but the third patient may be exposed to a higher x-ray dose than necessary.